List specimens collected to diagnose diseases caused by Intestinal Nematodes

List drugs of choice used to treat diseases caused by intestinal Nematodes

List tissue nematodes of medical importance

Learning Objectives cont….

These have separate-sexes and unsegmented roundworms

They have body cavities

They have complete digestive, reproductive and nervous systems

They include many parasitic species that infect humans.

Intestinal nematodes are round worms that infest the gastrointestinal tract of human and other animals.

They are characterized by having separate-sexes and unsegmented body, body cavities and complete digestive, reproductive and nervous systems.

Examples of intestinal nematodes include Ascaris lumbricoides, Trichuris trichiura,Necator americanus/ Ankylostoma duodenale (hook worm), Enterobius vermicularis,Trichuris trichiura and Strongiloides stercoralis

Hookworm

Ascaris lumbricoides

Strongyloides

Enterobius vermicuralis

Trichuris trichiura

A genus of parasitic nematode worms known as the “the giant intestinal round worm” belongs to Phylum Nemathelminthes, Class Nematoda, Order Ascaridida, Family Ascaridoidae Genus,: Ascaris and Species Ascaris lumbricoides.

The most common human helminthic infection.

Worldwide distribution.

Adult worm lives in the lumen of the small intestine (Jejunum) of man

Eggs are found in the faeces

The geographical distribution Ascaris lumbricoides

Large size of about 15 – 31cm length and 2-4 mm width, where females are relatively larger than males

The mouth is surrounded by three prominent lips

Males have the posterior end which is curved ventrally and the tail is curled with two prominent specules

The female tail is straight and pointed

Size 45-70 x 35-50 μm

There are three types of eggs

Fertilized egg

Decorticated and

Unfertilized

The fertilized egg is layered with outer albuminous covering which is coarselyn mammilated (= warty), thick egg shell, unsegmented embryo when laid.

Decoticated egg is devoid of the mammilated coat. Can easily be confused with the hookworm ova.

Unfertilized egg is has all the layers fused together and resemble vegetable fibres

Ascaris lumbricoides is transmitted through ingestion of eggs from food, water or fingers contaminated with faeces (Faecal oral route).

Adult worms live in the lumen of the small intestine

A female may produce approximately 200,000 eggs per day, which are passed with the faeces

Eggs are not infective immediately when passed in the faeces

Unfertilized eggs may be ingested but are not infective

Fertile eggs develop an embryo and become infective after 18 days to several weeks depending on the environmental conditions (optimum: moist, warm, shaded soil)

Infective eggs are swallowed

The egg hatches to release the larvae

The larvae invade the intestinal mucosa, and are carried via the portal vein to the systemic circulation, to the heart and eventually reach to the lungs (heart lung migration)

The larvae mature further in the lungs (10 to 14 days)

They break out from the blood capillaries and appear in the alveoli, ascend the inverted bronchial tree to the throat, and are swallowed again

Upon reaching the small intestine, they develop into adult worms in the period of 2 to 3 months after ingestion of the infective eggs

The male fertilizes the females and the female’s starts oviposition

Adult worms can live from 1 to 2 years

Ascaris lumbricoides causes

Ascaris pneumonitis (Loeffler’s syndrome)

Allergic manifestations (asthma)

Migrating larvae may reach the brain and cause encephalitis and meningitis

Adult worms can cause

Intestinal ascariasis

Malnutrition and general body debility

Intestinal obstruction

Appendicitis

Intestinal perforation

Migrating adults may reach the brain and cause encephalitis (rarely occurs)

Specimen

Stool

Technique

Microscopy

Wet mount and concentration method to detect ova

Clinical observation of worms passed

Albendazole

Mebendazole

Levamisole

Pyrantel pamoate

Piperazine

Phylum Nemathelminthes, Class Nematoda, Order Trichocephalida, Family Trichuridae Genus, Trichuris and Species Trichuris trichiura.

Trichuris trichiura has a worldwide distribution but it is more commonly found in tropical and subtropical countries with warm and moist climates.

The worm is wide spread in tropical Africa, South America and South East Asia.

EGGS: – the eggs are passed in human faeces, not infective when passed.

The infective egg containing larva – Found in Eggs in soil, water and on green vegetables

The geographical distribution Trichuris Trichiura (Whipworm)

The adult worm is greyish white or pinkish and lives in the caecum with the slender anterior end embedded in the mucosa between intestinal villi

The male

Is 3 – 4.5 cm long

Has a thin anterior portion which is half as long as the thicker posterior portion

The tail end is curved and terminates in a spicule

The female

Is 3.5 – 5.5 cm long

Has a thin anterior portion which is twice as long as the thick posterior half containing a stout uterus packed with eggs

The eggs

Measures 50×22 μm is brown and has characteristically barrel shaped

Has a single thick egg shell with a translucent plug at each end (bipolar plug)

It contains an unsegmented embryo at oviposition

Trichuris trichiura is transmitted through ingestion of eggs from food, water or fingers contaminated with faeces (Faecal oral route).

The undeveloped (unembryonated) eggs are passed with the stool

In the soil,

The eggs develop into a 2-cell stage,

An advanced cleavage stage,

Then develop an embryo

The whole process from oviposition to infective stage takes about 15 to 30 days

After ingestion, the eggs hatch in the small intestine, and release larvae

The larvae mature and establish themselves as adults in the colon

The adult worms (approximately 4 cm in length) live in the cecum and ascending colon

The adult worms are fixed in that location, with the anterior portions threaded into the mucosa

The females begin to oviposit 60 to 70 days after infection

Female worms in the cecum shed between 3,000 and 20,000 eggs per day

The life span of the adults is about 1 year

Adult worms cause

Intestinal Trichuriasis

Appendicitis

Dysentery

Rectal prolapse

Anaemia

Specimen

Stool

Technique

Microscopy

Wet mount and concentration method to detect ova

Clinical observation of worms when the rectum has prolapsed

Albendazole

Mebendazole

Levamisole

Pyrantel pamoate

Piperazine

Strongyloides stercoralis belongs to Phylum Nemathelminthes, Class Nematoda, Order Rhabditia Family Rhabditoidae Genus Strongyloides and Species S. stercoralis

Tropical and subtropical areas, but cases also occur in temperate areas (including the South of the United States).

The female adult worm lives in the mucous membrane of small intestine

The geographical distribution Strongiloides Stercoralis

Strongyloides stercoralis is a roundworm parasite that infects many warm-blooded organisms including humans, causing strongyloidiasis.

stercoralis parasitizes the tunnels in the mucosa of the small intestine.

Other hosts for Strongyloides infection include mammals, birds, reptiles and amphibians

Two species of Strongyloides can infect humans, S. stercoralis and S. fuelleborni.

Fuelleborni is however common in African primates where infection can be shared with humans.

Males are about 0.9 mm in length and females can be anywhere from 2.0 to 2.5 mm

Both male and female possess a tiny buccal capsule and cylindrical esophagus without a posterior bulb.

Their developmental forms consist of adult, rhabditiform larva and filariform larva (infective).

In the free-living stage, both sexes are rhabditiform larva.

Males can be distinguished from their female counterparts by two structures: the spicules and gubernaculums

It occurs in either of the two forms, parasitic forms and free living.

The larva of strongiloides has a notched tail (This can help in distinguishing it the larva of hookworm)

Transminision of Strongyloides stercoralis is by the infective filariform larvae in contaminated soil penetrating the human skin.

Sometimes auto infection occurs

Auto infection can result into overwhelming infection which can be life threateni

The Strongyloides life cycle is more complex than that of most nematodes with its alternation between free-living and parasitic cycles, and its potential for autoinfection and multiplication within the host.

Free-living Cycle.

The rhabditiform larvae passed in the stool

It can either molt twice and become infective filariform larvae (direct development)

Or molt four times and become free living adult males and females

Free living males and females mate and produce eggs

Eggs hatch to produce rhabditiform larvae

The rhabditiform larva can either develop into a new generation of free-living adults (as represented in ), OR

Rhabditiform larva develop into infective filariform larvae

The filariform larvae in contaminated soil penetrate the human host skin to initiate the parasitic cycle

The filariform larvae transported via the blood stream to the lungs where they penetrate the alveolar spaces; they are carried through the bronchial tree to the pharynx, are swallowed and then reach the small intestine

In the small intestine they molt twice and become adult female worms

The females live threaded in the epithelium of the small intestine and produce eggs

Eggs hatch and produce rhabditiform larvae and migrate to lumen

The rhabditiform larvae can either be passed in the stool to start the Free-living cycle OR

The rhabditiform causes autoinfection

In autoinfection, the rhabditiform larvae become infective filariform larvae.

The filariform larvae can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection).

In either case, the filariform larvae may follow the heart lung migration route, being carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine where they mature into adults.

Or they may disseminate widely in the body.

Strongyloides autoinfection may explain the possibility of persistent infections for many years in persons who have not been in an endemic area and of hyperinfections in immunodepressed individuals.

Diseases Caused by Strongiloides stercoralis

Strongiloidiosis that can manifest in the form of

Worm infestation in duodenum and jejunum leading to chronic diarrhoea

Skin rashes due to larvae

Blindness due to larvae migrating into the eyes

Viscera larva migrants due to autoinfection

Pulmonary and neurologic complications

Specimen

Stool

Technique

Microscopy

Wet preparation for larva

Invermectine

Mebendazole

Albendazole

Thiabendazole

Phylum Nemathelminthes, Class Nematoda, Order Strongylida, Family Ancylostomaidae Genus Hookworm and Species Ancylostoma duodenale and Necator americanus

The second most common human helminthic infection (after ascariasis).

Worldwide distribution, mostly in areas with moist, warm climate.

The geographical distribution and habitat of Hookworms

Both N. americanus and A. duodenale are found in Africa, Asia and the Americas.

Necator americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa, and southern Europe

The adult worm resides in small intestine of man particularly in jejunum

The Hookworms

Hookworms are parasitic round worms that lives in the small intestine of its host, which may be a mammal such as a dog, cat, or human.

Two species of hookworms which are pathogenic to human are

Ancylostoma duodenale

Necator americanus

Ancylostoma duodenale

Are small grayish white or pink with the head slightly bent in relation to the rest of the body. This bend forms a definitive hook shape at the anterior end for which hookworms are named.

They possess well developed mouths with two pairs of ventral teeth.

Males measure approximately one centimeter by 0.5 millimeter, the females are often longer and stouter.

Additionally, males can be distinguished from females based on the presence of a prominent posterior copulatory bursa.

Is very similar in morphology to Ancylostoma duodenale.

Is generally smaller than Ancylostoma duodenale with males usually 5 to 9 mm long and females about 1 cm long.

Possesses a pair of semi lunar cutting plates in the buccal capsule.

Additionally, the hook shape is much more defined in Necator than in Ancylostoma.

The eggs are oval or elliptical, measuring 60 μm by 40 μm, colorless, not bile stained with a single thin transparent hyaline shell membrane.

When released by the worm in the intestine, the egg contains an unsegmented ovum.

During its passage down the intestine, the ovum develops; thus the eggs passed in faeces have a segmented ovum, usually with 4 to 8 blastomeres.

As the eggs of both Ancylostoma and Necator (and most other hookworm species) are indistinguishable, to identify the genus, they must be cultured in the lab to allow larvae to hatch out.

Penetration of unbroken skin by filariform larva.

Ancylostoma may also be acquired by the oral route by direct ingestion of infective larvae contaminated fruits and vegetables.

Eggs are passed in the stool, and under favourable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days.

The released rhabditiform larvae grow in the faeces and/or the soil, and after 5 to 10 days (and two moults) they become filariform (third-stage) larvae that are infective.

These infective larvae can survive 3 to 4 weeks in favorable environmental condition

On contact with the human host, the larvae penetrate the skin and are carried through the veins to the heart and then to the lungs.

They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed.

The larvae reach the small intestine, where they reside and mature into adult.

Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host.

Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years.

Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle)

In addition, infection by A. duodenale may probably also occur by the oral and transmammary route

americanus, however, requires a transpulmonary migration phase.

Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle).

In addition, infection by A. duodenale may probably also occur by the oral and transmammary route.

americanus, however, requires a transpulmonary migration phase.

e4

Disease they Cause

Ground itch at the time of skin penetration: irritating vesicular rash limited to the site of invasion, usually in the sole of feet or hands

Pneumonia during heart lung migration

Iron deficiency anemia, secondary to loss of iron (and protein) in the gut

Iron deficiency anemia (caused by blood loss at the site of intestinal attachment of the adult worms) is the most common symptom of hookworm infection and can be accompanied by cardiac complications.

Gastrointestinal and nutritional/metabolic symptoms can also occur.

In addition, local skin manifestations (“ground itch”) can occur during penetration by the filariform (L3) larvae, and respiratory symptoms can be observed during pulmonary migration of the larvae

The diseases are called: Ancylostomiasis, necatoriasis, and hookworm infections associated with several conditions:

Microcytic, hypochromic anaemia of the iron-deficiency type

Ground itch (dermatitis) due to penetrating larvae through the skin

Bronchopneumonia due to migrating larvae in lungs

Haemorrhage in the intestinal mucosa

Specimen

Stool

Technique

Microscopy

Wet mount and concentration technique to detect ova.

Culture (Kato Katz technique) for recovery of rhabditiform larvae (but not routine)

Clinical to when the worms are passed

Albendazole

Mebendazole

Pyrantel pamoate

Phylum Nemathelminthes, Class Nematoda, Order Spirurida, Family Oxyuroidae Genus Enterobius and Species Enterobius vermicularis.

Enterobius vermicularis is a Worldwide, with infections more frequent in school- or preschool- children and in crowded conditions.

Enterobiasis appears to be more common in temperate than tropical countries.

The most common helminthic infection in the United States (an estimated 40 million persons infected).

The geographical distribution and habitat of Enterobius vermicularis

EGGS: – the eggs are passed in human faeces, not infective when passed.

The infective larva – Found in Eggs in soil, water and on green vegetables

Adult worm (female) resides in caecum and appendix of man.

The geographical distribution and habitat of Enterobius vermicularis

Female

They are small, 9-12 mm x 0.4 mm

Has a cervical alae (wing like expansion) at the anterior end

There is a bucal cavity that terminates into a prominent oesophageal bulb

Has a long pointed tail with eggs

o 2-5 mm with a curved tail and a single spicule

Males are seldom seen

Egg

o 50-54 x 20-27 μm with characteristic shape – flattened on one side. Almost colourless with bean-shaped double contour shell

Eggs of Enterobius vermicularis in wet mount

Eggs of Enterobius vermicularis in cellulose preparation

Ingestion of eggs from contaminated fingers, bedding and formites

Inhalation of eggs from dust

Autoinfection

Retroinfection

1Eggs are deposited on perianal folds. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area (Autoinfection).

2The ingested eggs hatch in the small intestine to produce larva 3.

4& 5The larva matures and become adult in the large intestine where the male fertilizes the female.

The female migrates to the perianal folds where deposit eggs on perianal skin folds.

The female worm dies after laying eggs.

These would be swallowed and follow the same development

Sometimes eggs hatch at the perianal area and the larva migrates to the caecum where they mature to become adults and fertilization takes place (Retroinfection)

Under optimal conditions, it takes 4 to 6 hours for the eggs become infective.

The time interval from ingestion of infective eggs to oviposition by the adult females is about one month.

The life span of the adults is about two months

Disease they Cause

Pruritus ani is the main symptom and varies from mild itching to acute pain which occurs mainly at night.

The pruritus provides scratching of the perianal region resulting in excoriation and secondary infection.

Vulvitis may be caused by pinworms entering the vulva causing a mucoid discharge and pruritus vulvi.

In young children severe infection can cause chronic diarrhoea, intestinal ulceration, and anaemia, weight loss and prolepses of the rectum.

Enterobiasis is frequently asymptomatic.

The most typical symptom is perianal pruritus, especially at night, which may lead to excoriations and bacterial super infection.

Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur.

Abdominal pain.

Scotch tape swab

Stool

Technique

Microscopy

Wet mount and concentration technique to detect ova

Examination of the tape swab for ova and adult worm

Albendazole

Mebendazole

Hookworm and Enterobius vermicularis are intestinal small round worms

Hookworm follows heart lung migration in its life cycle while Enterobius vermicularis follows direct life cycle without heart lung migration.

Hookworm is transmitted through skin penetration by filariform larvae in the soil

Enterobius vermicluaris is transmitted through

Ingestion of eggs from contaminated fingers, bedding, and formites

Autoinfection

Retroinfection

Ascaris lumbricoides and Trichuris trichiura are intestinal round worms which are transmitted through ingestion of eggs from food, water and fingers contaminated with faeces.

Acaris lumbicoides causes Ascariasis (Ascaris pneumonitis, allergic manifestations, encephalitis and meningitis).

The life cycle of Ascaris lumbricoides follows heart-lung migration.

Infection of Trichuris trichiura leads to dysentery and rectal prolapse.

Diagnosis of both Ascaris lumbricoides and Trichuris trichiura depend on recovery and identification of eggs in the faeces.

Strongyloides stercoralis is a roundworm parasite that infects many warm-blooded organisms including humans, causing strongyloidiasis

Transminision of Strongyloides stercoralis is primarily by the infective filariform larvae in contaminated soil penetrating the human skin.

Auto infection can result into overwhelming infection which can be life threatening.

Laboratory diagnosis is dependent on microscopic examination of stool to detect lar

What are the morphological characteristics of Ascaris lumbricoides?

What are the differences between ova of Ascaris lumbricoides and that of Trichuris trichiura?

What are the laboratory techniques used to identify both Ascaris lumbricoides and Trichuris trichiura?

What are the characteristics of Strongyloides stercoralis?

What are the three types of life cycles of Strongyloides stercoralis?

What is the Laboratory identification method for Strongyloides stercoralis?

What are the drugs of choice for Strongyloides stercoralis

What is the mode of transmission of hookworm?

Mention the most common complication of hookworm infection.

Mention drugs of choice for enterobiasis and hookworms.

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Mark, E.,V., James, B. L. (2010). Worm Book. Retrieved May 13th 2010 from http://www.wormbook.org/chapters/www_genomesStrongyloides/genomesStrongyloides. html.

Mike, S. (2004). Medical Entomology for Students. London: Oxford University Press

Monica, C. (1987). Medical Laboratory Manual for Tropical Countries (2nd Ed.). Volume 1, Oxford: ELBS Butterworth, Heinemann Ltd.

Monica, C. (1998). District Laboratory Practice in Tropical Countries. Part 1. Tropical Health Technology, Noida, India: Gapson Papers Ltd.

Monica, C. (2000). District Laboratory Practice in Tropical Countries. Part 2. Tropical Health Technology. UK: Cambridge University Press